I. Field of the Invention
This invention relates to a method of machining workpieces and to a form of vise for use therein.
II. Description of the Prior Art
In the art of machining workpieces, it is known that there is numerical-control equipment which makes it possible to produce large numbers of identical pieces in a given amount of time, with any desired features (drilled or bored holes, milled or shaped slots, chased threads, etc.) being produced rapidly, accurately, and errorlessly, and with a minimal generation of scrap. A workpiece which is to be machined is positioned accurately within a vise, and then the numerical-control equipment takes over, bringing against the piece to be worked upon the necessary and appropriate tools for performing the desired machining operation or operations. The numerical-control equipment is, of course, largely limited to performing operations upon a face of the workpiece which is presented towards the tool or tools to be used. Whenever the piece which is to be made is such that all of the required operations can be done upon just one face of the workpiece, the numerical-control equipment and the precision vises known in accordance with the prior art usually yield very satisfactory results. The numerical-control equipment is suitably programmed so that the necessary operations are done in a predetermined sequence, and after the equipment has gone through one cycle of its operation, one finished piece is removed.
There are, however, some product pieces which need to be made by working with tools being brought to bear first upon one side or face of the workpiece and then upon an adjacent or an opposite face of the workpiece.
While a workpiece is being worked upon, it needs to be securely held, and this means that, at the least, the sides or faces thereof which are presented towards the vise or other means within which the workpiece is held are unavailable for being worked upon.
Thus, even with some relatively expensive and sophisticated numerical-control equipment, equipment which is capable of machining a piece from the front, the back, and the top thereof, the sides which are presented towards the vise are not available for machining without removing the piece from the equipment and later conducting a separate operation. More often, the numerical-control equipment is even simpler and less sophisticated, being able to machine only the front or only the front and the top; if there are things to be done to any pair of opposite faces of the workpiece, it takes two set-up operations to get the numerical-control equipment to make the desired product piece.
Moreover, there is the problem that pieces which have been subjected to the first operation need to be stored or stockpiled for as long as the first operation is being conducted. It is desirable, of course, to spend a minimum of time upon the changeover from doing the first operation to doing the second, or vice versa, but with the equipment and methods available prior to the present invention, it has usually been necessary to have such changeovers, back and forth, at rather frequent intervals, because of having only a limited amount of space available for storage of partly finished pieces.
There has distinctly been a need for a method and equipment such that it is possible, when desiring to make a product piece which requires machining directed at more than one face of the workpiece which is to be machined, to insert into the numerical-control equipment a pair of pieces, one having a first orientation and another having a second and different orientation, so that when the numerical-control equipment is permitted to go through one cylce of operation, it performs, in effect, the complete machining of a piece, doing the first half of what is necessary to one workpiece while doing the second half of what is necessary to its vise-mate. This greatly improves the productivity of the numerical-control equipment. What is needed is a suitable precision vise which has the capability of holding not one workpiece but two. There has not hitherto been available to the metal working art, to the applicants' knowledge, any suitable two-piece-holding precision vise for use with numerical-control equipment. Various forms of precision vises are commercially available, but none of the commercially available vises is as suitable as that of the present invention.
It might appear that the problem could be solved with the use of a precision vise adapted to hold one object in such a way that it holds two workpieces which are differently oriented, either with a suitable jig or fixture in the nature of a spacer there between, or even merely with one workpiece pressed against another one which is differently oriented. As is well appreciated by those skilled in the art, such an approach does not yield satisfactory results, since it does not provide for having the pieces which are being machined suitably located with respect to a reference point. Any deviation in the desired dimension through which the workpiece is being held, of one piece, the other piece, or of both, will cause undesirable deviations in the location of the features being machined into both workpieces.
The precision vises which are now commercially available have a drawback, in that when the vise is in operation, the shaft which has on its exterior the jaw-advancing screw is put into compression, rather than into tension, when the jaws are being tightened. Putting the screw shaft into compression introduces bending forces which tend to cause the screw shaft and the base both to become bowed, which is a source of inaccuracy. It is desirable that the screw shaft be pulled straight and not pushed into bowing.
Those familiar with the arts of building and using precision vises are familiar with the concept, shown in the expired Muggli, et al., U.S. Pat. No. 2,880,638, of using a hemispherical segment inserted between the jaw-advancing nut and the jaw bit to which the jaw plates are attached, in order to obtain a self-alignment feature.
The idea, in the art of precision vises, for being able to mount jaw plates selectively on either of two mounting faces of the jaw, in order to be able to accomodate pieces of different overall length, is shown in U.S. Pat. No. 3,397,880.